Thank you for the kind replies.
This work was motivated by a problem I had with a marketing company in Vancouver, where the database administrator was frequently interrupted by requests to fix their broadcasts. Although there weren't a lot of errors given the size of the weekly mailouts, each one was a serious annoyance that consumed a lot of time.
It took a while before I realized that their problems were simply anomalies in directed graphs, which made things easier to visualize.
But for really large graphs, we might need a more efficient way to process them.